Myosin light chain phosphorylation in human myometrial smooth muscle cells.
Ca2+/calmodulin-dependent phosphorylation of the 20-kDa regulatory light chain of myosin is of signal importance in the initiation of contraction in a number of smooth muscle tissues. In this investigation, we evaluated the relationship between intracellular free Ca2+/concentration [( Ca2+]i) and the extent of myosin light chain phosphorylation in cultured human myometrial smooth muscle cells. Treatment of myometrial cells with ionomycin caused a concentration- and time-dependent increase in [Ca2+]i and phosphorylation of myosin light chain. Temporally, the increases in light chain phosphorylation and [Ca2+]i in response to ionomycin were similar. In myometrial cells treated with ionomycin (10(-5) M) for 10 s, [Ca2+]i increased from 138 to 800 nM; in these same cells, myosin light chain phosphorylation increased from 5% to a maximum value of 54%. Half-maximal phosphorylation of myosin light chain was attained at 300 nM [Ca2+]i. Treatment of myometrial smooth muscle cells with prostaglandin (PG) F2 alpha (10(-8) M) and PGE2 (10(-8) M) caused a proportionate increase in [Ca2+]i and myosin light chain phosphorylation. In addition, [Ca2+]i and myosin light chain phosphorylation increased in response to oxytocin and angiotensin II. These findings indicate that a number of uterotonic agents effect an increase in [Ca2+]i, which in turn causes phosphorylation of myosin light chain. Furthermore, the concentration of Ca2+ in the cytoplasm is a primary determinant for myosin light chain phosphorylation in human myometrial smooth muscle cells.
Mackenzie
L W
LW
Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas, Southwestern Medical Center, Dallas 75235.
Word
R A
RA
Casey
M L
ML
Stull
J T
JT
D000804:Angiotensin II / Q000494:pharmacology; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D015237:Dinoprost / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D010121:Oxytocin / Q000494:pharmacology; D010766:Phosphorylation; D013050:Spectrometry, Fluorescence
D001572:Benzofurans; D005456:Fluorescent Dyes; D015879:Myosin Subfragments; D000804:Angiotensin II; D010121:Oxytocin; D015759:Ionomycin; D015237:Dinoprost; D015232:Dinoprostone; D002118:Calcium; D016257:Fura-2